This IRC avenue is all about shifting the blame to ATC's.
You cannot take 107 controllers off the roster, away from seperating traffic, and just expect the remaining 750 or so to cover their absence with overtime.
It takes up to 18 months to get an ATC their first rating. And usually another 6 to 12 months to get any other ratings in that airspace group. After 4 years, TFN should know the lead-in times required. But the "restructure" went ahead anyway. (Johnnie was on his way out, and AsA had to get the AWA's in.....)
It won't matter what the IRC defines reasonable overtime as. AsA - probably because publicly they use statistics across service delivery lines (which include 3 or more ATC airspace groups each) to average the overtime required to a better sounding extra 1.1 shifts (or something like that) per ATC per month - But AsA needs to acknowledge that some groups need almost no overtime, and others for example have their rosters published with empty shifts to be filled in advance - BEFORE ANYONE GOES SICK!!
FFS - it's a safety critical job! Making ATC's work more overtime is going to increase their fatigue, impair their performance, and increase the risk of something going wrong!